Influence of pre-existing structures on the emplacement and deformation of Late-Jurassic rift related magmatism in Newfoundland, Canada

Abstract

The Notre Dame Bay Magmatic Province (NDBMP) comprises a suite of Late Jurassic (Tithonian), rift-related alkaline mafic intrusions in north-central Newfoundland, Canada. This field-based study focuses on the Leading Tickles area, where the gabbroic Budgell’s Harbour Stock (BHS) and radial lamprophyre dykes intrude strongly folded and faulted Ordovician back-arc volcanic and sedimentary host rocks. The primary objective was to understand how pre-existing structures influenced the emplacement and post-intrusion deformation of the NDBMP. This thesis employs a comprehensive methodology, including field mapping, thin section analysis, stereographic projections, kinematic and dynamic analysis, GIS visualization, and 3D analog modelling to analyze the interactions between pre-existing structures and the NDBMP. The results reveal that lamprophyres preferentially exploited pre-existing Paleozoic Appalachian structures associated with the Iapetus Suture Zone. Furthermore, magmatic activity weakened and deformed the host rocks, leading to the reactivation of Silurian thrust faults that deformed the lamprophyres post-intrusion. Movement along Luke’s Arm Fault Zone (LAFZ) in Leading Tickles may indicate a broader reactivation of the Iapetus Suture in northern Newfoundland during the Mesozoic. The variation in lamprophyre mineralogies and the presence of numerous radial dyke clusters suggest multiple magma sources coinciding with regional antiforms.